docs(web): point showcase footer migration link to v1.6 -> v1.7

cut-release.ps1 version-bumps the web/index.html pins (softwareVersion, hero badge, install snippets) but does not touch content links. The footer still pointed at the v1.5->v1.6 guide; update it to the new v1.6->v1.7 migration guide so the deployed site is consistent after the v1.7.0 release.

Author: DemchaAV

web/index.html

@@ -394,7 +394,7 @@ <h3>Markdown-aware bodies</h3>
     <p>
       <a href="https://github.com/DemchaAV/GraphCompose">GitHub</a> &middot;
       <a href="https://github.com/DemchaAV/GraphCompose/blob/main/CHANGELOG.md">Changelog</a> &middot;
-      <a href="https://github.com/DemchaAV/GraphCompose/blob/main/docs/roadmaps/migration-v1-5-to-v1-6.md">v1.5 &rarr; v1.6 migration</a>
+      <a href="https://github.com/DemchaAV/GraphCompose/blob/main/docs/roadmaps/migration-v1-6-to-v1-7.md">v1.6 &rarr; v1.7 migration</a>
     </p>
   </footer>